An optical layered body is commonly provided on the outermost surface of an image display device, such as cathode ray tube displays (CRT), liquid crystal displays (LCD), plasma displays (PDP), and electroluminescent displays (ELD), for antireflection.
Such an optical layered body for antireflection suppresses reflection of images and lowers the reflectance by light diffusion or light interference.
A known optical layered body for antireflection is an antiglare film including a transparent substrate and an antiglare layer with surface roughness provided on the surface of the transparent substrate. Surface roughness on the surface of such an antiglare film diffuse external light, thereby preventing reduction in visibility due to reflection of external light and reflection of images.
An optical layered body is commonly provided on the outermost surface of an image display device, and therefore is required to have a hard-coating property for avoiding scratches formed during handling thereof.
Conventionally known antiglare films are formed, for example, by applying a resin containing a filler such as silicon dioxide (silica) to the surface of a light-transmitting substrate to form an antiglare layer thereon (see Patent Literatures 1 and 2, for example).
Surface roughness of such antiglare films is formed by the following methods. Particles such as aggregative silica particles are aggregated to form surface roughness on the surface of the antiglare layer. An organic filler or the like having a particle size of not smaller than the thickness of a coating film to be formed is added to a resin to form surface roughness on the layer surface. An organic filler or the like having a particle size of not larger than the thickness of a coating film to be formed is added to a resin, so that surface roughness is formed on the layer surface by curing shrinkage of the resin at positions corresponding to the organic filler. A film having surface roughness on its surface is laminated to transfer projections and depressions. Each of these methods is employed alone or in combination with others.
These conventional antiglare films produce light diffusion/antiglare effects by surface features of the antiglare layer. Accordingly, to enhance the antiglare effect, projections and depressions need to be enlarged. An enlarged projections and depressions, however, increase the haze value of the film to cause white muddiness, problematically lowering the contrast of the displayed image.
Further, conventional antiglare films have flicker, so-called scintillation as disclosed in Patent Literature 3, on the film surface, problematically lowering the visibility of the display screen.
To solve the above problems, an antiglare film in which a hard coat layer and an antiglare layer are laminated is known (see Patent Literature 4, for example). An antireflection film having such a layered configuration suppresses scintillation and white muddiness, while maintaining the hard-coating property and the antiglare property. Such a film, however, is thick, failing to satisfy the recent demands for thinner antiglare films.
Accordingly, there has been a demand for an antireflection film including an antiglare layer with a monolayer structure that sufficiently suppresses scintillation and white muddiness, while maintaining the hard-coating property and antiglare property.